Pulverulent coating agents based on blocked aromatic diisocyanates

ABSTRACT

Object of the invention is a pulverulent coating agent curing at a temperature above 130*C comprising (a) at least one polymer containg hydroxyl groups and having a softening point of at least 40*C, and (b) an with Epsilon -caprolactam masked product consisting of an aromatic polyisocyanate and a dihydric alcohol.

United States Patent [191 de Cleur et al.

[451 July 8,1975

[ PULVERULENT COATING AGENTS BASED ON BLOCKED AROMATIC DIISOCYANATES [75] Inventors: Eckhard de Cleur, Duisburg; Rolf Dhein; Hans Rudolph; Hans-Joachim Kreuder, all of Krefeld, Germany [73] Assignee: Bayer Aktiengesellschaft,

Leverkusen, Bayerwerk, Germany [22] Filed: Mar. 22, 1973 [21] Appl. No.: 343,798

[30] Foreign Application Priority Data Mar. 28, 1972 Germany 2215080 [52] US. Cl. 260/77.5 TB; 117/17; 260/22 TN [51] Int. Cl. C08G 22/32; BOSB 5/00 .[58] Field of Search 260/775 TB [56] References Cited UNITED STATES PATENTS 2,698,845 1/1955 Mastin et a1 260/775 TB 2,801,990 8/1957 Seeger et al. 260/775 TB 3,621,000 11/1971 Schmelzer et a1. 260/775 TB 3,659,003 4/1972 Johnson et al. 260/77.5 TB 3,660,355 5/1972 Johnson et a1 260/77.5 TB 3,660,359 5/1972 Labana 260/775 TB 3,676,402 7/1972 Matsui et a1. 260/775 TB 3,676,405 7/1972 Labana 260/775 TB 3,703,499 11/1972 Lindemann. 260/77.5 AT 3,711,571 1/1973 Farah 260/775 TB 3,721,647 3/1973 Mazzeo et a1 260/775 TB 3,748,315 7/1973 Wooster et al. 260/77.5 TB 3,770,703 11/1973 Gruber et al. 260/775 TB Primary ExaminerH. S. Cockeram Attorney, Agent, or FirmConnol1y and Hutz [57] ABSTRACT Object of the invention is a pulverulent coating agent curing at a temperature above 130C comprising (a) at least one polymer containg hydroxyl groups and having a softening point of at least 40C, and (b) an with e-caprolactam masked product consisting of an aromatic polyisocyanate and a dihydric alcohol.

7 Claims, No Drawings PULVERULENT COATING AGENTS BASED ON BLOCKED AROMATIC DIISOCYANATES This invention relates to pulverulent coating agents adapted for use by spreading on a substrate and curing at an elevated temperature.

According to German Offenlegungsshrift No. 1,957,483 and German Offenlegungsschrift No. 20 64 098 pulverulent mixtures of high-melting polyester resins and/or polyethers and/or polyurethanes and/or polyester-urethanes and/or alkyd resins and/or urethane-alkyd resins and/or vinyl polymers and/or epoxide resins, containing hydroxyl groups, can be used, in combination with e-caprolactam-masked polyisocyanates, as powder lacquers.

The polyisocyanates masked with e-caprolactam can also be e-caprolactam-masked adducts of more-thandihydric alcohols with polyisocyanates, such as, for example, the tris-e-caprolactam-masked adduct of 1 mol of trimethylolpropane with 3 mols of toluylenediisocyanate and 3 mols of caprolactam.

This invention now provides a pulverulent coating agent curing at a temperature above 130C, preferably between 150C and 210C, comprising a. at least one polymer containing hydroxyl groups and having a softening point of at least 40C;

b. an e-caprolactam-masked adduct of an aromatic polyisocyanate preferably an aromatic diisocyanate, a dihydric alcohol, preferably a dihydric ether-alcohol, and e-caprolactam.

The agent may include also a catalyst and further customary additives.

The invention also provides a process for forming a coating on a substrate comprising spreading the pulverulent coating agent of the invention on the substrate and heating to above 130C, preferably between 150 and 210C, to cure the agent and form a continuous coating.

1n the coating agent according to the invention, the e-caprolactam-masked adduct, component (b), acts as a cross-linking agent for the polymeric component (a).

The adducts of diols, polyisocyanates and e-caprolactam are preferably manufactured with the molar ratio (calculated for diols, diisocyanates and e-caprolactam) of 1 to 0.5 (diol) to 2 (diisocyanate) to 2 3 (e-caprolactam), with the number of equivalents mols) of e-caprolactam to be employed preferably being so calculated in each case that it does not exceed the difference between the isocyanate equivalents and OH equivalents. If polyisocyanates with more than 2 NCO groups per molecule are used instead of, or in addition to, diisocyanates, correspondingly recalculated molar ratios or equivalent ratios apply.

In the coating agents according to the invention, the component (b) should preferably in each case be present in amounts of between about 10% by weight and about 100% by weight, preferably between about 20% by weight and about 50% by weight, relative to the The pulverulent coating agents according to the invention are distinguished by a combination of good properties.

They have a storage stability of more than 10 days at 4045C and can be processed at a stoving temperature of only C, Without the use of additional catalysts, to give lacquerings of good elasticity and good resistance to acetone. Under comparable conditions, this is only possible with the powder lacquer binders of German Offenlegungsschrift No. 1,957,483 (Example 1) under substantially less favourable conditions (stoving temperature 200C).

The result is surprising since for powder lacquer binders with storage stabilities above 40C, which are intended to give elastic, acetone-resistant lacquerings, only high-melting polyesters in combination with strongly elasticising crosslinking agents, for example based on hexamethylenediisocyanate or isophoronediisocyanate, are suitable for use; these combinations can however only be processed to give good lacquerings, even in the presence of catalysts, at minimum stoving temperatures of 180C, whilst in the absence of catalysts stoving temperatures of at least 200C are needed.

The unique properties of crosslinking agents based on e-caprolactam-masked adducts of aromatic polyisocyanates, diols and e-caprolactam, namely an improvement in the storage stability, high elasticity of stoved powder lacquer films and the possibility of achieving optimum results already at stoving temperatures of 170C, opens up a multiplicity of possible combinations of these crosslinking agents with polyester resins and/or polyethers and/or polyurethanes and/or polyesterurethanes and/or alkyd resins and/or urethane-alkyd resins and/or vinyl polymers and/or epoxide resins which contain hydroxyl groups.

Examples of aromatic isocyanates which are suitable for the manufacture of the new crosslinking agents are: toluylenediisocyanates, naphthylenadiisocyanates diphenylmethane-4,4-diisocyanate and triphenylmethane-4,4,4 '-triisocyanate.

Products of the general formula are suitable for use as diol components; in these,

R denotes an optionally substituted aliphatic radical with 2 to 8 carbon atoms in the chain, of which up to 2 carbon atoms can be replaced by hetero-atoms or groups containing hetero-atoms,

wherein R can represent hydrogen or any C -C -all yl, phenyl, toluyl or benzyl groups.

As examples of diols there may be mentioned: ethylene glycol, propanediols, butanediols, hexanediols, diethylene glycol, triethylene glycol, thiodiglycol or N-methyldiethanolamine. Ether-alcohols, such as diethylene glycol or triethylene glycol, are employed as preferred diols. Mixtures of diols can also be used.

The procedure followed for the manufacture of the crosslinking agents according to the invention, based on the abovementioned E-caprolactam-masked adducts, is generally such that in the end product the molar ratio of diisocyanates to'diols is 2.0 to 4.0, preferably 2.1 to 2.7. The remaining equivalentsof isocyanate groups are blocked with -caprolactam. It is also possible to manufacture products which are not completely blocked with caprolactam; however, care must be taken that not more than .one isocyanate group should be present free per molecule of crosslinking agent, since otherwise crosslinking can already occur on mixing the crosslinking agents with the resins containing hydroxyl groups. I

Lacquerings with particularly good levelling are in particular obtained with the crosslinking agents according to the invention based. on diethylene glycol, toluylene diisocyanate and e-caprolactam in the molar ratio of 0.7 -0.9 (diethylene glycol) 2 ('toluylenediisocyanate) 2 (e-caprolactam).

The crosslinking agents according to the invention can be manufactured by first reacting the diisocyanates at 40C to 160C, preferably at 80 to 140C, with the diols and subsequently carrying out=-the reaction with e-caprolactam in the same temperature range. It is also possible to proceed conversely and first to react the dir'isocyanatesat 40 to 120, preferably at 80 to 120,

with caprolactam and subsequently at 80 to 160 with the diols.rA combination of both processes, namely first to react the diisocyanates with apart of the diols or of the caprolactam, then with a part of the caprolactam or of the diols, and then again with the remaining part of the diols or of the caprolactam, is also possible.

The polyester resins and/or polyurethanes and/or '"polyester-urethanes and/or alkyd resins and/or urethane-alkyd resins, containing hydroxyl groups, which according to the invention are to be used in combina- 'tion with the new crosslinking agents can be manufactured in accordance with processes which are in themselves known, preferably from cyclic polycarboxylic J acids, such as phthalic acid, isophthalic acid, terephthalic acid, benzene-1,2,4-tricarboxylic acid, 3,6- dichlo'rophthalic acid, tetrachlorophthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, endomethylenetetrahydrophthalic acid or, where these are accessible, their anhydrides or lower alkyl esters, and tri- I differential thermoanalysis.

ary catalysts, and through suitable choice of the COOH/OH ratio end products are obtained of which the hydroxyl numbers lie between 4.0 and 250, preferably'between and 150. They hydroxyl numbers of the remaining abovementioned polymers should lie in the same range.

Usable polyvinyl resins containing hydroxyl groups, with hydroxyl numbers ofbetween 40 and 250, preferably between 40 and 150, are manufactured in a manner which is in itselfknown by copolymerisation of the corresponding monomers, for example hydroxy-propyl- (meth)-acrylic acid ester, hydroxy-ethyl(meth)acry1ic acidester, ethyl acrylate, butyl acrylate, .2-ethylhexy1 acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, styrene, a-methylstyrene, vinylt olue ne, acrylonitrile, acrylamide, vinyl acetate, acrylic acid and m ethacrylic acid, in the presence of initiatorsand regulators.- Polyethers which can be used, for example from ethylene oxide and/or propylene oxide are also known.

The situation is similar with polyepoxide resins. The

most customary are reaction products of 2,2-bis (4- hydroxyphenyD-propane (bisphenol Aland epichlorohydrin. v V i The softening points of the mixtures .ofresin and crosslinking agentmust be so low that they can be processedat temperatures of between 80 and 130 with the additives necessary for the manufacture of the coating agents according to the invention. On the other hand, the softening points of the mixtures must be so high that the coating agents according to the invention can be ground to give free-flowing powders of particle size. 20 to 120 11., which do not form lumps. in practice this means. that the resins employed have softening points of between 40 and about 140, as determined by The coating agents can be produced in suitable mix- I ing apparatuses, for example in stirred kettles or mixing mellitic anhydride, as well as from diols, such as ethyltoluylenediisocyanates, naphthyldiisocyanates, diphen ylmethane-4,4'-diisocyanate, dicyclohexylmethane- 4,4'-diisocyanate and triphenylmethane4,4 ',4 triisocyanate can be used, whilst amongst monoisocyanates ethylisocyanate or phenylisocyanate can be used.

The polyesters are manufactured in-a manner which is in itself known, by esterification or transesterification, if appropriate in the presence of customscrews. Customary additives, such as'pigments, levelling agents, fillers and catalysts, for example the compounds mentioned in German Pat. Spec. No. 946,173, can also be added. a

The crosslinking agent itself is preferably employed in such amounts that the ratio of hydroxyl groups of the resin: masked optionally: free NCO groups of the crosslinking agent is between 0.5 and 6.0, preferably between 0.7 and 1.5. I

The products according to the invention can be con verted into powders, the free-flowing characteristics of which remain preserved even on prolonged storage at temperatures of about 40C. These powders can be applied to substrates iii the customary manner, especially in accordance with the'electi'ostatic powder spraying process. 4

a On heating to temperatures above C, preferably between 150C and 210C, the lacquer films rapidly 1 curefto give coatings having very good properties. i Shaped articles which can be coated may consist for example of metal, glasses and ceramics.

- MANUFACTUR'E'OF THE CROSSLINKING I AGENTS- E XA MPLE1' r (Molar ratio: 0.86 diol 2.0 diisocyanate 2.0 e-caprolactam) 25,056 parts by, weight mols) 'of toluylcnediisocyanate (Desmodur T 65, a commercial product consisting of an isomer mixture of 2,4- and 2,6- toluylenediiisocyanate) are warmed to 90C in a stirred kettle, whilst passing nitrogen over the niateriai. A total of 16,372 parts by weight (145 rnols) of E-caprolactarn reached. 212 parts by weight 01' dietlaylene glycol are then added dropwise and the temperature is raised to 140C. The mixture is further stirred until the NCO value is 2%.

is added in several portions over the course of one hour 5 Characteristic Data and the mixture is stirred at 90C until an NCU value Viscosity: '73 seconds (55% strength in ethyl glycol of approx. 16% is found. A total of 6,552 parts by acetate accord g to 1931753111) weight (62 mols) oi diethylene glycol is added droplime NCO: 2% wise, in several portions, over the course of 4 hours, UMP i ON EXPERH ENT 2 and the temperature is at same time raised to 140C. The mixture further stirred until the NCO (ii/101m M001 12212) content is about 0-5 2% A crosslinlaing agent is manufactured analogously to Characteristic Data Comparison Experiment i from 336 parts by weight of Viscosity sewnds sit'engtl'l in fithill glycsi bexarnethylenediisocyanate, 22.6 parts by Weight of acetate, according 0 19W 15 e-caprolactam and 10.6 parts by weight of diethylene free NCU: 0.5 2% glycol. The product is liquid at room temperature. softening point (8.19.) approx. 70C characteristic D (according to the {UTA willed! C Mackenzie, Viscosity: 17 seconds (55% strength in ethyl glycol Differential "11 her-mall Analysis, London, 1970, Vol. r rw gcgoyding to MN 5321 1) Y 1. free NCO: 2%

. EXAMFLE 2 Manufacture of Powder Lacquerings (M0121T ratio; 036220220) The parts by weight, indicated below, of a polyester F manufactured from bis-oxyethylbisphenol A, glycerine 940 Parts by Welghl 0K Desmaflur T w g and terephthalic acid in accordance with known prom 80C After adding 123 pal-ts by Weight of dlemylana cesses (acid number: 10; Ui-l' number: 48 softening glycol in portions, the NCO value is approx. 34%. The point approx. 0 (UTA); Viscosity: 155 sficonds (50% iemperawre is raised to 19006, 610 pal-fishy welghad strength in xyiene/n-butanol, 9:1, according to DlN Caprolaclam are added m several portions and 53211)) are intimately mixed with the crosslinking mixture is further stirred until the NCQ value is approx. agents 0f Exampk 1 in pm Case of powder lacquer A During the addition of a fume" fi and of Comparison Experiment 1 in the case of powder weight of diethylene glycoi the temperature is raised to gficquei. B a Yuma titanium dioxide pigmflmt and a level 140C and the mixture is run out after an NCO value h {g agsm based on cenulosfi (a Exodus? Of Messrs. 0f 20/517135 been machfid Bombers) on an edge runner niiii and subsequently Characteristi 9am q homogenised in an extruder at 90 1 10C. After cool- Viscosity: 70 Seconds Simngth in em); glycol ing, the ribbon is ground by means of a pinned disc mill a fi according to DEN 53,211) to a particle size of less than 100 ,u. The particles thus free NCQI 0.5 produced are applied to the substrate by means of an 40 electrostatic powder spraying installation at lcV and EXAMPLE 3 then stoved for 20 minutes at 170C.

(Molar ratio: 1.0 g 2.0 2 2.0)

870 parts by weight of Desrnodur T are warmed Pam to C. 295 parts by weight of hexane-1,6-diol are 45 powder by Weight p by weight Levelling Tit) added in portions over the course of 1 /2 hours and at Lacquer Polyester Of Crosslinkins Agent A s Agent from Example the same time tne temperature is allowed to rise to C. When an NCO value of approx. 18% is mea- A 100 30 (Example 1 1.3 s sured, 565 parts by weight of e-caprolactarn added 3 30 L3 87 in several portions and the mixture is ated to C. 56 r l After reaching 05-12% of NCO the mixture run out.

Characteristic Data powder lacquers A and B can be stored for at Viscosity: 36 Seconds sfiengfil in Ethyl glycll least 10 days at 40 45C without losing their freeacfiialie, according DEN 53,21 flowing character; they give lacquerings having the folirce NCU: 05 55 iowing properties:

Powder Stoving Time- Coating Erichsen Acetone Resist- Lacquer Temperature Thickness Deepance drawing Value A 20, C 70 [-L 10 mm resistant B 20, 170C 70 o 1.0 mm not resistant CUMPAlulS-ON EX ERll i lT 1 Lacquering B is only eiastic after a stoving time or" 30 34 minutes at C with zinc l -l-ethyl-lJ-phenyl- (Molar ratio: 122:2)

88 parts by weight of l-isocyanato-3- (isocyanatomethyl)-3,5,5trimethylcyciohexane are reacted in portions with 452 parts by weight of e-caprolactam at 80 until an NCC content of approx. 13% is dithiocarbaniate as the catalyst or a stoving time of 15 minutes at 200C without a Powder lacquer binders manufactured from the above-rnentioned polyester and Comparison Experi- 2 are not stable on storage.

It can be seen from the present comparison that only the powder lacquer A according to the invention displays a combination of improved properties, namely a storage stability of at least 10 days at 40 45C and stoving temperatures, without catalyst, of 170C, as well as acetone resistance and high elasticity of the lacquerings stoved at 170C. lf powder lacquer B is used, stoving temperatures of 170C only yield non-elastic lacquerings which are not resistant to acetone.

Analogous processing of the crosslinking agent described in Comparison Experiment 2 does not achieve the objective, since a corresponding mixture with the above-mentioned polyester (100 parts by weight of polyester 30 parts by weight of crosslinking agent) already forms lumps at room temperature. If less than 30 parts by weight, for example 10 parts by weight, of crosslinking agent of Comparison Experiment 2 are used, powder lacquers can admittedly be produced with the abovementioned polyester; however, lacquerings stoved for minutes at 170C are non-elastic and not resistant to acetone.

What we claim is:

l. A pulverulent solvent-free coating agent curable at a temperature of above 130C. comprising a. at least one polymer containing hydroxyl groups and having a softening temperature of at least 40C. and b. a crosslinking amount of an adduct of an aromatic diisocyanate, a dihydric alcohol, and e-caprolac;

tam, said dihydric alcohol being selected from the group consisting of ethylene glycol, propanediol, butanediol, hexanediol, diethyleneglycol, triethyleneglycol, thiodiglycol, N- methyldiethanolamine and mixtures thereof and said dihydric alcohol, diisocyanate and e-caprolactam being present in said adduct in the molar ratio of 0.5-1: 2:2-3.

2. The coating agent of claim 1 wherein said dihydric alcohol is diethyleneglycol or triethyleneglycol.

3. The coating agent of claim 1 wherein said adduct contains diethylene glycol, toluylene diisocyanate and e-caprolactam in a molar ratio of 0.7-0.9: 20:20.

4. The coating agent of claim 1 wherein component (b) is present in an amount of 10 to 100% by weight based on the weight of component (a).

5. The coating agent of claim 1 wherein component '(b) is present in an amount of 20 to 50% by weight based on the weight of component (a).

6. The coating agent of claim 1 wherein the ratio of hydroxyl groups present in component (a) to the total number of masked and any free isocyanate groups of component (b) is between 0.5 and 6.0.

'7. The coating agent of claim 1 wherein the ratio of hydroxyl groups present in component (a) to the total number of masked and any free isocyanate groups of 

1. A PULVERULENT SOLVENT-FREE COATING AGENT CURABLE AT A TEMPERATURE OF ABOVE 130*C. COMPRISING A. AT LEAST ONE POLYMER CONTAINING HYDROXYL GROUPS AND HAVING A SOFTENING TEMPERATURE OF AT LEAST 40*C. AND B. A CROSSLINKING AMOUNT OF AN ADDUCT OF AN AROMATIC DIISOCYANATE, A DIHYDRIC ALCOHOL, AND $-CAPROLACTAM, SAID DIHYDRIC ALCOHOL BEING SELECTED FROM THE GROUP CONSISTING OF ETHYLENE GLYCOL, PROPANEDIOL, BUTANEDIOL, HEXANEDIOL, DIETHYLENEGLYCOL, TRIETHYLENEGLYCOL, THIODIGLYCOL, NMETHYLDIETHANOLAMINE AND MIXTURES THEREOF AND SAID DIHYDRIC ALCOHOL, DIISOCYANATE AND $-CAPROLACTAM BEING PRESENT IN SAID ADDUCT IN THE MOLAR RATIO OF 0.5-1: 2:2-3
 2. The coating agent of claim 1 wherein said dihydric alcohol is diethyleneglycol or triethyleneglycol.
 3. The coating agent of claim 1 wherein said adduct contains diethylene glycol, toluylene diisocyanate and epsilon -caprolactam in a molar ratio of 0.7-0.9: 2.0:2.0.
 4. The coating agent of claim 1 wherein component (b) is present in an amount of 10 to 100% by weight based on the weight of component (a).
 5. The coating agent of claim 1 wherein component (b) is present in an amount of 20 to 50% by weight based on the weight of component (a).
 6. The coating agent of claim 1 wherein the ratio of hydroxyl groups present in component (a) to the total number of masked and any free isocyanate groups of component (b) is between 0.5 and 6.0.
 7. The coating agent of claim 1 wherein the ratio of hydroxyl groups present in component (a) to the total number of masked and any free isocyanate groups of component (b) is between 0.7 and 1.5. 